Catalytic domain of the Protein Tyrosine Kinase, Insulin-like Growth Factor-1 Receptor. Protein Tyrosine Kinase (PTK) family; Insulin-like Growth Factor-1 Receptor (IGF-1R); catalytic (c) domain. The PTKc family is part of a larger superfamily that includes the catalytic domains of other kinases such as protein serine/threonine kinases, RIO kinases, and phosphoinositide 3-kinase (PI3K). PTKs catalyze the transfer of the gamma-phosphoryl group from ATP to tyrosine (tyr) residues in protein substrates. IGF-1R is a receptor tyr kinases (RTK) that is composed of two alphabeta heterodimers. Binding of the ligand (IGF-1 or IGF-2) to the extracellular alpha subunit activates the intracellular tyr kinase domain of the transmembrane beta subunit. Receptor activation leads to autophosphorylation, which stimulates downstream kinase activities and biological function. IGF-1R signaling is important in the differentiation, growth, and survival of normal cells. In cancer cells, where it is frequently overexpressed, IGF-1R is implicated in proliferation, the suppression of apoptosis, invasion, and metastasis. IGF-1R is being developed as a therapeutic target in cancer treatment.